1. Field of the Invention
This invention relates generally to methods and apparatus for making magnetic heads, and more particularly to methods and apparatus for controlling the lapping of a slider based on an amplitude of a readback signal produced from an externally applied magnetic field.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (e.g. a disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
The dimensions of magnetic heads are shrinking rapidly as the recording density of magnetic disks continues to increase. To ensure optimal magnetic performance, these magnetic heads require tight dimension controls at both the wafer manufacturing and slider fabrication levels. Magnetic heads are formed during the wafer manufacturing process where widths, gaps, and other dimensions of the magnetic heads are defined. During such process, a wafer is typically cut into many individual sliders, each of which carries a magnetic head and associated read sensor. The sliders are mechanically lapped or polished with use of a lapping plate to achieve a flat and smooth surface finish for good mechanical performance. The lapping also defines the proper heights for the magnetic head, especially the read sensor's height (a.k.a. the “stripe height”) for good magnetic performance.
Traditionally, slider fabrication was monitored and controlled with the use of Electrical Lapping Guides (ELGs). ELGs are typically formed at a kerf area of the wafer in between sliders for the sole purpose of lapping control. With today's magnetic heads, however, the alignment error between the ELG and the read sensor becomes significant relative to the stripe height. Therefore, the resistance of the read sensor may be utilized to directly control the lapping process to achieve a very tight read sensor resistance distribution. Achieving such tight resistance distribution, however, does not guarantee optimal magnetic performance. Most variations in read sensors (e.g. variations in the read gap thickness, mean-read-width or MRW, film quality, hard bias quality, etc.) are fixed from the wafer manufacturing prior to the lapping process. Thus, achieving tight resistance distribution only eliminates one of several variations which contribute to the degradation of magnetic performance. One of the key indicators of a read sensor's performance is its response to external magnetic fields, specifically its readback signal amplitude and asymmetry. Amplitude measures the read sensor's sensitivity to the magnetic field, and asymmetry measures the shape of the response.
Accordingly, what are needed are ways in which to control the lapping of sliders to optimize the performance of read sensors.